“Empty as a bass drum,” the detective assured him complacently.  “He turned it upside down and shook it.”

“Then what became of them?” demanded Mr. Latham.

“Became of what?”

“The diamonds, man—­what became of the diamonds?”

“You didn’t mention any diamonds to me except those five the other day,” the detective reminded him coldly.  “Your instructions were to find out all about this man—­who he is, what he does, where he goes, and the rest.  This is my preliminary report.  You didn’t mention diamonds.”

“I didn’t know he would have them,” Mr. Latham exploded irascibly.  “That empty gripsack, man—­when he left here he carried millions—­I mean a great quantity of diamonds in it.”

“A great quantity of —­,” the detective began; and then he sat up straight in his chair and stared at Mr. Latham in bewilderment.

“If the gripsack was empty when he was on the car,” Mr. Latham rushed on excitedly, “then don’t you see that he got rid of the diamonds somehow from the time he left here until you saw that the gripsack was empty?  How did he get rid of them?  Where does he keep them?  And where does he get them?”

Mr. Birnes closed his teeth grimly and his eyes snapped. Now he knew why Mr. Wynne had taken that useless cab ride up Fifth Avenue.  It was to enable him to get rid of the diamonds!  There was an accomplice—­in detective parlance the second person is always an accomplice—­in that closed cab!  It had all been prearranged; Mr. Wynne had deliberately made a monkey of him—­Steven Birnes!  Reluctantly the detective permitted himself to remember that he didn’t know whether there was anybody in that cab or not when Mr. Wynne entered it, and—­and—!  Then he remembered that he did know one thing—­the number of the cab!

He arose abruptly, with the light of a great determination in his face.

“Whose diamonds were they?” he demanded.

“They were his, as far as we know,” replied Mr. Latham.

“How much were they worth?”

Mr. Latham looked him over thoughtfully.

“I am not at liberty to tell you that, Mr. Birnes,” he said at last.  “There are a great number of them, and they are worth—­they are worth a large sum of money.  And they are all unset.  That’s enough for you to know, I think.”

It seemed to be quite enough for Mr. Birnes to know.

“It may be that I will have something further to report this evening,” he told Mr. Latham.  “If not, I’ll see you to-morrow, here.”

He went out.  Ten minutes later he was talking to a friend in police headquarters, over the telephone.  The records there showed that the license for the particular cab he had followed had been issued to one William Johns.  He was usually to be found around the cabstand in Madison Square, and lived in Charlton Street.

CHAPTER VI